The present invention relates generally to providing network services such as load balancing, packet filtering or Network Address Translation (NAT). More specifically, network services are provided using service managers and forwarding agents that are integrated into a routing infrastructure.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be useful to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
Providing network services using a distributed network of forwarding agents improves reliability. In addition a backup scheme for service managers is needed to ensure that the forwarding agents can receive instructions even when a service manager fails. Ideally, such a scheme would not require configuration or reconfiguration of forwarding agents to allow a backup service manager to assume control from a failed primary service manager.
A system that includes a primary service manager and one or more backup service managers is disclosed. The primary service manager sends wildcard affinities to forwarding agents specifying sets of flows to be serviced by the primary service manager. Each backup service manager likewise sends wildcard affinities to forwarding agents that specify flows that the backup service manager will service if the primary service manager fails. The backup wildcard affinities have a lower backup precedence and the forwarding agent is configured to look for wildcard affinities that have a higher backup precedence first. Thus the backup wildcard affinities remain unused on the forwarding agent until the primary service manager fails and the backup service manager is needed.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication lines. Several inventive embodiments of the present invention are described below.
In one embodiment, a fault tolerant method of providing a network service includes receiving a first criteria specifying a first set of flows from a first service manager at a forwarding agent. The first criteria specifies an expiration time interval. The first criteria is stored on the forwarding agent. A second criteria is received that specifies a second set of flows from a second service manager at the forwarding agent. The second set of flows includes flows that are in the first set of flows and the second criteria is designated as a lower priority criteria. The second criteria is stored on the forwarding agent. The first criteria is deleted from the forwarding agent upon the expiration of the expiration time interval. A packet is received that belongs to a flow that is included in the first set and the second set. It is determined that the packet matches the second set ant the packet is forwarded to the second service manager.
In another embodiment, a fault tolerant method of providing a network service includes receiving a first criteria specifying a first set of flows from a first service manager at a forwarding agent wherein the first criteria specifies an expiration time interval. The first criteria is stored on the forwarding agent. A second criteria is received that specifies a second set of flows from a second service manager at the forwarding agent wherein the second set of flows includes flows that are in the first set of flows and wherein the second criteria is designated as a lower priority criteria. The second criteria is stored on the forwarding agent. The first criteria is deleted from the forwarding agent upon the expiration of the expiration time interval. A packet is received that belongs to a flow that is included in the first set and the second set. It is determined that the packet matches the second set and the packet is forwarded to the second service manager.
In another embodiment, a forwarding agent configured to provide a network service according to instructions from a service manager includes a service manager interface operative to receive a first criteria specifying a first set of flows from a first service manager. The first criteria specifies an expiration time interval. The service manager interface is also operative to receive a second criteria specifying a second set of flows from a second service manager. The second set of flows includes flows that are in the first set of flows and the second criteria is designated as a lower priority criteria. A memory is configured to store the first criteria and the second criteria. A processor is operative to check the stored first criteria and to delete the stored first criteria upon the expiration of the expiration time interval.
In another embodiment, a redundant service manager system configured to provide instructions to a forwarding agent includes a primary service manager configured to send a first criteria specifying a first set of flows to a forwarding agent. The first criteria specifies an expiration time interval so that the first criteria may be deleted from the forwarding agent upon the expiration of the expiration time interval. The primary service manager includes a processor for processing packets belonging to the first set. A backup service manager is configured to send a second criteria specifying a second set of flows to the forwarding agent. The second set of flows includes flows that are in the first set of flows and the second criteria is designated as a lower priority criteria.